The present invention relates to a method and an apparatus for regulating the braking force of motorcycles.
From Federal Republic of Germany OS 35 30 280 a method is known for the anti-lock braking of a motor vehicle. In that case, by the change in the volume of a three-dimensionally closed system, for instance by displacement of a pressure-relief piston, the brake pressure in the wheel cylinder of the overbraked wheel which tends towards locking is reduced.
Upon extreme braking decelerations two-wheel vehicles tend to lift up at the rear since the entire weight of the vehicle is shifted to the front wheel. By the loss of the ground contact force and thus all lateral guidance forces, the rear wheel is no longer able to impart sufficient stability in direction to the braked vehicle. In extreme cases, the center of gravity can be shifted upward and forward by a slight tipping of the vehicle around the front axle, whereby even greater tipping is induced, which, in its turn, results in an even more unfavorable shifting of the center of gravity. This self-excitation effect has the result that a vehicle which is in danger of lifting off can, within a short period of time, rise by a large angle of tip (greater than 45.degree.) and suddenly be no longer capable of being controlled by the driver. In addition to this, the strong deceleration of the vehicle which can cause excessive tipping occurs predominantly in a dangerous situation which generally already requires the entire concentration of the driver.
The danger of the vehicle lifting off is further increased by new tire characteristics, the .mu.-slip curve of which achieve a pronounced maximum, and by anti-lock systems which continuously utilize the maximum slip curve.
From Federal Republic of Germany OS 21 33 547 a braking force control for motor vehicles is known in which an additional logical coupling is provided which lowers the pressure on the front-wheel brakes if a signal indicating ground adherence of the rear wheels no longer occurs within a given waiting period.
Such a regulation of the braking force is perhaps suitable for utility vehicles since, due to their great weight, a considerable time is available in order to recognize the danger of the lifting off of the rear axle and counteract it.
Furthermore, four-wheel motor vehicles have only one brake system; in other words, upon actuation, the front axle and the rear axle are braked simultaneously. If the brake is actuated strongly, which on good gripping ground can lead to a lifting-off of the back of the vehicle, high braking forces are definitely present also on the rear wheels and immediately cause strong locking tendencies and make the lifting off clearly visible merely by observation of the lack of restarting of the rear wheel.
For motorcycles, such a regulating of the braking force, however, is unsuitable since the conditions are much more complicated. On the one hand, the lifting off takes place substantially faster due to the smaller masses while, on the other hand, motorcycles have two brake circuits which are actuatable independently of each other.
It is thus possible to decelerate a vehicle so greatly solely with the front wheel brake that lifting off of the rear occurs while, entirely independently thereof, the rear wheel brake can control the variation of the speed of the rear wheel. In combination with a non-disengaged drive, practically any speeds of the rear wheel can be brought about.
Upon recognition of the lift-off, all relevant wheel speed patterns must as far as possible be clearly recognized, i.e., on the one hand, all cases of lift-off which actually occur during each braking must be reliably recognized, while, on the other hand, lift-off should never be noted if not present, in order to avoid unjustified underbraking.